Cross-correlation between the dipole-dipole interaction and the Curie spin relaxation. The effect of anisotropic magnetic susceptibility

Cross-correlated relaxation caused by the interference of nuclear dipole–dipole interaction and the Curie spin relaxation (DD–CSR cross relaxation) is generalized to treat the case of anisotropic magnetic susceptibility, including the important case where the latter originates from zero-field splitting. It is shown that the phenomenon of DD–CSR cross relaxation is absolutely general and to be expected under any electronic configuration. The results of the generalization are presented for a model system, and the consequences for paramagnetic metalloproteins are illustrated with an example of cerium(III)-substituted calbindin. The effects of the magnetic anisotropy are found to be substantial.